That could only explain why the new new file is smaller. What about the changed bitrate?

Above looks to me that the the bitrates are called for the whole ts.

the last 2 ffmpeg -i outputs show "max 25000" for the actual mpeg2video stream.

I expect that the variable bitrates shown in the first output are accurate for the video stream. but nowhere else really contradicts them.

When doing just ffmpeg -i infile bitrate estimations are just based on looking at a small bit of the start of the file, so the fact that the last output "19490" is less than the 19626.9 that is visible in the first output I expect is just due to that.